我在指纹演示中有一些错误

Question

I was trying to make fingerprint demo. However, the following exception has occurred. I get NullPointerException on my button click

01-04 11:35:18.647 3295-3295/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.letsnurture.fingerprint, PID: 3295
java.lang.NullPointerException: Attempt to invoke virtual method 'void javax.crypto.Cipher.init(int, java.security.Key)' on a null object reference
  at com.letsnurture.fingerprint.MainActivity.initCipher(MainActivity.java:179)
  at com.letsnurture.fingerprint.MainActivity.access$000(MainActivity.java:45)
  at com.letsnurture.fingerprint.MainActivity$1.onClick(MainActivity.java:131)
  at android.view.View.performClick(View.java:5198)
  at android.view.View$PerformClick.run(View.java:21147)
  at android.os.Handler.handleCallback(Handler.java:739)
  at android.os.Handler.dispatchMessage(Handler.java:95)
  at android.os.Looper.loop(Looper.java:148)
  at android.app.ActivityThread.main(ActivityThread.java:5417)
  at java.lang.reflect.Method.invoke(Native Method)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

  01-04 12:08:55.382 1836-2383/? E/MDM: [83] b.run: Couldn't connect to Google API client: ConnectionResult{statusCode=API_UNAVAILABLE, resolution=null, message=null}

My code below:

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.app.KeyguardManager;
import android.content.Intent;
import android.content.SharedPreferences;
import android.hardware.fingerprint.FingerprintManager;
import android.security.keystore.KeyGenParameterSpec;
import android.security.keystore.KeyPermanentlyInvalidatedException;
import android.security.keystore.KeyProperties;
import android.util.Base64;
import android.util.Log;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;


import java.io.IOException;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.UnrecoverableKeyException;
import java.security.cert.CertificateException;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.inject.Inject;


public class MainActivity extends AppCompatActivity {


    private static final String TAG = MainActivity.class.getSimpleName();

    private static final String DIALOG_FRAGMENT_TAG = "myFragment";
    private static final String SECRET_MESSAGE = "Very secret message";
    /** Alias for our key in the Android Key Store */
    private static final String KEY_NAME = "my_key";

    @Inject
    KeyguardManager mKeyguardManager;
    @Inject
    FingerprintManager mFingerprintManager;
    @Inject
    FingerprintAuthenticationDialogFragment mFragment;
    @Inject
    KeyStore mKeyStore;
    @Inject
    KeyGenerator mKeyGenerator;
    @Inject
    Cipher mCipher;
    @Inject
    SharedPreferences mSharedPreferences;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        Button purchaseButton = (Button) findViewById(R.id.purchase_button);
        mKeyguardManager = (KeyguardManager) getSystemService(KEYGUARD_SERVICE);
        if (!mKeyguardManager.isKeyguardSecure()) {
            // Show a message that the user hasn't set up a fingerprint or lock screen.
            Toast.makeText(this,
                    "Secure lock screen hasn't set up.\n"
                            + "Go to 'Settings -> Security -> Fingerprint' to set up a fingerprint",
                    Toast.LENGTH_LONG).show();
            purchaseButton.setEnabled(false);
            return;
        }

        //noinspection ResourceType
        mFingerprintManager = (FingerprintManager) getSystemService(FINGERPRINT_SERVICE);
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.USE_FINGERPRINT) != PackageManager.PERMISSION_GRANTED) {
            // TODO: Consider calling
            //    ActivityCompat#requestPermissions
            // here to request the missing permissions, and then overriding
            //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
            //                                          int[] grantResults)
            // to handle the case where the user grants the permission. See the documentation
            // for ActivityCompat#requestPermissions for more details.
            return;
        }
        if (!mFingerprintManager.hasEnrolledFingerprints()) {
            purchaseButton.setEnabled(false);
            // This happens when no fingerprints are registered.
            Toast.makeText(this,
                    "Go to 'Settings -> Security -> Fingerprint' and register at least one fingerprint",
                    Toast.LENGTH_LONG).show();
            return;
        }
        try {
            try {
                createKey();
            } catch (NoSuchProviderException e) {
                e.printStackTrace();
            }
        } catch (KeyStoreException e) {
            e.printStackTrace();
        }
        purchaseButton.setEnabled(true);
        purchaseButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                findViewById(R.id.confirmation_message).setVisibility(View.GONE);
                findViewById(R.id.encrypted_message).setVisibility(View.GONE);



                // Set up the crypto object for later. The object will be authenticated by use
                // of the fingerprint.
                try {
                    if (initCipher()) {

                        // Show the fingerprint dialog. The user has the option to use the fingerprint with
                        // crypto, or you can fall back to using a server-side verified password.
                        mFragment.setCryptoObject(new FingerprintManager.CryptoObject(mCipher));
                        boolean useFingerprintPreference = mSharedPreferences
                                .getBoolean(getString(R.string.use_fingerprint_to_authenticate_key),
                                        true);
                        if (useFingerprintPreference) {
                            mFragment.setStage(
                                    FingerprintAuthenticationDialogFragment.Stage.FINGERPRINT);
                        } else {
                            mFragment.setStage(
                                    FingerprintAuthenticationDialogFragment.Stage.PASSWORD);
                        }
                        mFragment.show(getFragmentManager(), DIALOG_FRAGMENT_TAG);
                    } else {
                        // This happens if the lock screen has been disabled or or a fingerprint got
                        // enrolled. Thus show the dialog to authenticate with their password first
                        // and ask the user if they want to authenticate with fingerprints in the
                        // future
                        mFragment.setCryptoObject(new FingerprintManager.CryptoObject(mCipher));
                        mFragment.setStage(
                                FingerprintAuthenticationDialogFragment.Stage.NEW_FINGERPRINT_ENROLLED);
                        mFragment.show(getFragmentManager(), DIALOG_FRAGMENT_TAG);
                    }
                } catch (NoSuchPaddingException e) {
                    e.printStackTrace();
                }
            }
        });

    }

    /**
     * Initialize the {@link Cipher} instance with the created key in the {@link #createKey()}
     * method.
     *
     * @return {@code true} if initialization is successful, {@code false} if the lock screen has
     * been disabled or reset after the key was generated, or if a fingerprint got enrolled after
     * the key was generated.
     */

    private boolean initCipher() throws NoSuchPaddingException {
        try {
            mKeyStore.load(null);
            SecretKey key = (SecretKey) mKeyStore.getKey(KEY_NAME, null);
           // mCipher = Cipher.getInstance("DES/CBC");
            mCipher.init(Cipher.ENCRYPT_MODE, key);
            return true;
        } catch (KeyPermanentlyInvalidatedException e) {
            return false;
        } catch (KeyStoreException | CertificateException | UnrecoverableKeyException | IOException
                | NoSuchAlgorithmException | InvalidKeyException e) {
            throw new RuntimeException("Failed to init Cipher", e);
        }
    }

    public void onPurchased(boolean withFingerprint) {
        if (withFingerprint) {
            // If the user has authenticated with fingerprint, verify that using cryptography and
            // then show the confirmation message.
            tryEncrypt();
        } else {
            // Authentication happened with backup password. Just show the confirmation message.
            showConfirmation(null);
        }
    }

    // Show confirmation, if fingerprint was used show crypto information.
    private void showConfirmation(byte[] encrypted) {
        findViewById(R.id.confirmation_message).setVisibility(View.VISIBLE);
        if (encrypted != null) {
            TextView v = (TextView) findViewById(R.id.encrypted_message);
            v.setVisibility(View.VISIBLE);
            v.setText(Base64.encodeToString(encrypted, 0 /* flags */));
        }
    }

    /**
     * Tries to encrypt some data with the generated key in {@link #createKey} which is
     * only works if the user has just authenticated via fingerprint.
     */
    private void tryEncrypt() {
        try {
            byte[] encrypted = mCipher.doFinal(SECRET_MESSAGE.getBytes());
            showConfirmation(encrypted);
        } catch (BadPaddingException | IllegalBlockSizeException e) {
            Toast.makeText(this, "Failed to encrypt the data with the generated key. "
                    + "Retry the purchase", Toast.LENGTH_LONG).show();
            Log.e(TAG, "Failed to encrypt the data with the generated key." + e.getMessage());
        }
    }

    /**
     * Creates a symmetric key in the Android Key Store which can only be used after the user has
     * authenticated with fingerprint.
     */
    public void createKey() throws KeyStoreException, NoSuchProviderException {
        // The enrolling flow for fingerprint. This is where you ask the user to set up fingerprint
        // for your flow. Use of keys is necessary if you need to know if the set of
        // enrolled fingerprints has changed.

      //  mKeyStore=(KeyStore)getSystemService(Context);
        mKeyStore = KeyStore.getInstance(KeyStore.getDefaultType());

        try {

            mKeyStore.load(null);
            // Set the alias of the entry in Android KeyStore where the key will appear
            // and the constrains (purposes) in the constructor of the Builder
             mKeyGenerator = mKeyGenerator.getInstance("AES", "BC");
            mKeyGenerator.init(new KeyGenParameterSpec.Builder(KEY_NAME,
                    KeyProperties.PURPOSE_ENCRYPT |
                            KeyProperties.PURPOSE_DECRYPT)
                    .setBlockModes(KeyProperties.BLOCK_MODE_CBC)
                    // Require the user to authenticate with a fingerprint to authorize every use
                    // of the key
                    .setUserAuthenticationRequired(true)
                    .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_PKCS7)
                    .build());
            mKeyGenerator.generateKey();
        } catch (NoSuchAlgorithmException | InvalidAlgorithmParameterException
                | CertificateException | IOException e) {

        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.action_settings) {
            Intent intent = new Intent(this, SettingsActivity.class);
            startActivity(intent);
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}                                                                                                                         

Answer 1

I tried the same demo and it works for me.

I think you should consider whether those inject annotation work for you. If they don't work, you have to initialize those instances by yourself by using "new" followed by the constructor. Otherwise you'll get that null object reference error.